In a conventional hydrocarbon liquid fuel carburetor for an internal combustion engine, a fuel regulating needle is used to control the flow of fuel or fuel and air mixture from the carburetor fuel chamber to the air intake passageway. A threaded shaft portion of a metal fuel regulating needle valve is screwed into a threaded bore formed in a metal carburetor body to project a valve tip of the needle valve from a valve chamber to an outlet passage. However, when the threaded bore is machined in the carburetor body, chips from machining in the threaded bore often remain therein and hinder a smooth screwing of the fuel regulating needle valve into the threaded bore.
In addition, due to the small size of the threads on the needle valve and in the bore of the carburetor body, it is difficult to achieve desired manufacturing tolerances. Any play in the tolerances may allow leakage between the two sets of threads. In addition, any play in the tolerance allows an undesirable axially shifting of the threaded valve needle which may change the fuel efficiency settings of the carburetor from its desired factory settings and allows undesirable evaporative emissions.
Furthermore, limiter caps mounted on the head of the fuel regulating needle valve may introduce certain complications. Limiter caps have recently been mandated in various jurisdictions to prevent the end user from easily adjusting the fuel needle valves excessively far from the manufacture's desired settings. These limiter cap; are commonly placed on the head of the fuel needle valve by a snap fit or press fit. As the caps are pressed onto the heads, axial force and radial force may displace the tip end needle from its desired position. Accordingly, accurate regulation may be hindered. The tip of the needle valve may be inclined and a lesser amount of fuel may flow from the valve chamber to the outlet passage as compared to a straight mounted tip of the needle valve. Furthermore, because of the diminutive dimension of the needle tip and the bore about the needle tip, a mere translational displacement of the needle tip from its radially central position may change the turbulence and other flow characteristics such that the flow rate may be undesirably changed from the desired setting.
Environmental efforts are also directed to minimize fuel evaporative emission which not only wastes fuel but may also have detrimental effects on air quality.
What is needed, in view of the above described problem, is a carburetor with a fuel regulating needle valve that is free from fuel leakage from the valve chamber to the exterior, or air leakage from the exterior to the valve chamber. Furthermore, what is needed is a fuel regulating needle that is firmly supported against vibrations and recovers from side and axial extended forces exerted thereon.
What is also needed is a carburetor with a fuel regulating needle that is screwed into a plastic retainer and a metal collar which are interference fitted in an unthreaded cylindrical bore in a carburetor body, thereby eliminating the need of machining the threaded bore within the carburetor body.